1. Field of the Invention
This invention relates to a wireless magnetic resonance imaging (MRI) scanner (data acquisition unit) and to a method of operation of the scanner, using unlicensed spectrum for a local oscillator for upconversion.
2. Description of the Prior Art
MRI scanners use a combination of a strong constant magnetic field (B0) from a superconducting magnet which is modified by gradient fields generated by gradient coils, together with a rotating magnetic field (B1) from a radio frequency (RF) antenna to excite nuclear magnetic resonances in the body that generate short term RF signals that are received to build up a tomographic image.
All current-generation MRI scanners employ arrays of local coils mounted in close proximity to the scanned patient to receive the RF with maximum possible signal to noise ratio (SNR). The coils that receive signals from the back of the patient are mounted in the patient table. Coils that receive signals from the front of the patient are arranged into ‘blankets’ that are carefully placed over the patient. Associated with each blanket is typically a flexible cable containing one co-axial line for each local coil. The cables potentially interact with the B1 field and with the signals generated from the patient so ‘traps’ (high impedance sections) must be included at regular (typically λ/8) intervals. These add cost and inconvenience to the structure.
In use, the requirement to connect the cables and sterilize them between scanning one patient and the next leads to increased down-time between scans. It is therefore desirable that the cables be eliminated. However, a wireless solution permitting the cables to be eliminated also ideally substantially satisfies all the requirements of the existing system, particularly in the area of noise figure.